For many photonic products based on a silicon-on-insulator (SOI) opto-electronics platform, photonic components such as lasers, active optical devices and passive optical devices are mounted on (or integrated within) the same SOI substrate as the associated optical waveguides. In some cases, the electrical integrated circuits (ICs) used to control the lasers and other active optical devices are also mounted on/integrated within the common SOI substrate.
For any component with an optical “surface” (e.g., lasers, lenses, waveguide endface, etc.), dust and water condensation collecting on the optical surface will degrade the performance of the component, causing the optical signal entering or exiting the surface to scatter and reduce the power remaining along the optical signal path. Additionally, some active components (such as laser diodes and detectors) require a stringent operating environment for long-term reliability. Dust and water condensation are known to degrade the performance of these devices, leading to premature failure.
In order to protect a laser (or other critical component(s)) from dust/condensation, one prior art approach is to house these devices in a sealed environment (such as a hermetic package). As a general practice, hermetic sealing is relatively expensive and is not considered as a preferred alternative for use in high volume, consumer applications.
One non-hermetic prior art arrangement for protecting components from dust and water condensation utilizes a “cap” that is attached to and sealed around the perimeter of the SOI substrate. The cap is generally formed of a polymer material and is usually attached to the SOI substrate using adhesives or solders. FIG. 1 is a side view of an SOI photonics platform including this prior art type of cap. FIG. 1 shows an SOI photonics platform 1 including a silicon substrate layer 2, a buried oxide layer 3 and a relatively thin silicon surface layer 4 (hereinafter referred to as SOI layer 4). Optical waveguides are generally formed within SOI layer 4. In this particular configuration, a laser diode 5 is disposed within an etched region formed through SOI layer 4 and buried oxide layer 3 so as to be placed upon silicon substrate 2. An optical detector 6 is positioned behind laser diode 5 (used in this case as a backface monitor). A lensing arrangement 7 is positioned along the output signal path from laser diode 5 and is used to focus the propagating optical signal into an optical waveguide 8 formed within SOI layer 4. A set of electrical contacts 9 to both laser diode 5 and detector 6 are wire bonded to bond pads 10 placed above the interlayer dielectric (ILD) layer 11 of SOI photonic platform 1.
As shown in FIG. 1, a cap 20 is disposed to cover and encapsulate the optical and electrical components included within the SOI photonics platform 1. An adhesive/epoxy 22 is used to attach cap 20 to the platform. Cap 20 is generally formed of a polymer material and is suitable for preventing dust, liquids and other particulate matter from entering the structure and interfering with the operation of the optical components.
While the arrangement of FIG. 1 is considered an improvement in terms of protecting the sensitive optical devices to an extent, it is still possible for moisture to penetrate through the cap, allowing water to condense inside the enclosure. Thus, a need remains for an encapsulation arrangement of SOI-based photonic structures that does not require the use of a hermetic seal to prevent the build-up of condensation within the package.